In a needle loom for weaving a slide-fastener stringer, warp yarns for the support tape and warp yarns for tying-in of the coupling element are guided to form sheds, weaving needles being used to pick weft yarns for the support tape and synthetic resin monofilament yarn forming the coupling element through the sheds.
A weaving needle reciprocates continuously between an outside position and an inside position and is operative to loop the synthetic resin monofilament yarn around a former for forming the coupling members. A row of these coupling members is formed continuously from the latter yarn, the coupling members of such row each comprising a coupling head and connected arms or shanks which form a coupling loop and being joined together by connecting parts. The said row of coupling members is tied into the evolving support tape by the tying-in warp yarns and support tape weft yarns.
The tension of the infed synthetic resin monofilament yarn is adjusted by driven feed rolls and is so influenced by the reciprocation of the weaving needle that a tension peak is produced in the outside position of the weaving needle, in which position the synthetic resin monofilament yarn is drawn onto the former. The term "slide fastener strip" denotes the unit comprising a support tape and a row of coupling members. More particularly, it may be used here as synonomous with the term "stringer" referring to two slide fastener strips associated with one another for a slide fastening action by the movement of a slider and which can be produced simultaneously with coupling member rows which are coupled together during weaving.
In this case, the former for the coupling members is an elongated needle-shaped component which is mounted self-supportingly (German patent document No. 2 540 272).
Another possibility, disclosed by Europatent document No. 0 124 129, is to use a former which is relatively short and includes a hook disposed on a swing arm. As a rule, only a single slide fastener strip is produced in this way. A second such strip is operatively associated with the first strip elsewhere and at a different time. The coupling members which have been formed on the former are continuously drawn or pushed off the former as weaving continues.
The steps known from these patent documents produce closure members and rows thereof whose dimensions, including pitch, are defined with sufficient accuracy. However, the tolerances of the coupling heads and coupling loops are excessive. Satisfactorily shaped coupling heads are not readily obtainable. The excessive tolerances described may impair the transverse tensile strength and the ability of a slide fastener to withstand opening when subjected to bending and kinking. So that closer tolerances can be observed, particularly with respect to the coupling heads, it is conventional to pre-stamp coupling heads on the infed plastics monofilament yarn, with detriment to the actual weaving operation and to the rate of weaving.